Method to achieve the use of an external metric as the primary tie-breaker in intermediate system to intermediate system (isis) route selections

ABSTRACT

A method, apparatus and computer program product for providing the use of an external metric as the primary tie-breaker in ISIS route selections is presented. A set of routes are identified that are to be advertised by the router as external routes within a network. The routes are advertised by the router using a Type Length Variable (TLV), wherein the TLV contains metric information to be used as a first tiebreaker when selecting routes. The network is running an Intermediate System To Intermediate System (ISIS) protocol. The TLV includes a 32-bit or a 64-bit administrative tag sub-TLV, the TLV comprising TLV#135, TLV#235, TLV#236, and TLV#237.

BACKGROUND

Open Shortest Path First (OSPF) is a link-state routing protocol forInternet Protocol (IP) networks. OSPF uses a link state routingalgorithm and falls into the group of interior routing protocols,operating within a single autonomous system (AS). OSPF is an interiorgateway protocol that routes Internet Protocol (IP) packets solelywithin a single routing domain (autonomous system). OSPF gathers linkstate information from available routers and constructs a topology mapof the network. The topology determines the routing table presented tothe Internet Layer which makes routing decisions based solely on thedestination IP address found in IP packets.

OSPF detects changes in the topology, such as link failures, veryquickly and converges on a loop-free routing structure quickly. OSPFcomputes the shortest path tree for each route using a shortest pathfirst algorithm. The OSPF routing policies used to construct a routetable are governed by link cost factors (external metrics) associatedwith each routing interface. Cost factors may be the distance of arouter (round-trip time), network throughput of a link, or linkavailability and reliability, expressed as simple unitless numbers. Thisprovides a dynamic process of traffic load balancing between routes ofequal cost.

Another interior routing protocol is Intermediate System To IntermediateSystem (ISIS). ISIS is an interior gateway protocol, designed for usewithin an administrative domain or network. ISIS determines the bestroute for packets through a packet-switched network. ISIS is alink-state routing protocol, operating by reliably flooding link stateinformation throughout a network of routers. Each ISIS routerindependently builds a database of the network's topology, aggregatingthe flooded network information. Like the OSPF protocol, ISIS computesthe best path through a network. Packets are then forwarded, based onthe computed ideal path, through the network to the destination.

Routing protocols like ISIS and OSPF use internal cost to theadvertising router as the primary tie-breaker when making routeselection decisions. When the same route is advertised by multiplerouters, the route from the router that has the lowest internal cost(Layer 1 (L1) cost or internal gateway Protocol (IGP) cost) is accepted.Sometimes network operators may want route selection not to be based onthe internal cost, but instead to be based on an externally defined costmetric that they control before the routes are injected into the IGP.One of the primary reasons to do this is to achieve consistentprimary/backup destination behaviors for traffic going out of thenetwork (through firewalls for example) irrespective of the topology orpath costs internal to the network.

OSPF has a standard defined way for advertising routers to identify aroute type as internal or external and for external routes using theexternal metric as the primary tie-breaker during route selection.

SUMMARY

Conventional mechanisms such as those explained above suffer from avariety of deficiencies. Currently OSPF has a standardized way to selectroutes based on external cost and is supported by most router vendors.Similar or identical support is not available using ISIS. Workaroundsusing route-policies and metric manipulations have drawbacks. Currentcommercial practice is to use route-policies on the receiving routersand/or manipulate the ISIS link metric to force route selections in aspecific manner.

The use of route-policies on the receiving routers and manipulation ofISIS link metrics is not a true solution. Some of the problemsassociated with this conventional approach are that such an approachimpacts more than just the routes that user might want to select basedon external cost. Another problem associated with the above describedconventional approach is that the approach requires configuration ofroute policies on all the receiving routers and requires prior knowledgeof the system-id/IP address of the advertising routers to configure theroute-policy. Yet another problem is that the conventional approach mayrequire prior knowledge of the specific target routes for use in theroute policies, in general requiring too much advance knowledge of routeand router addresses makes a dynamic routing protocol less useful.Generally, the use of route-policies is heavy handed and cumbersomeconfiguration wise.

Embodiments of the invention significantly overcome such deficienciesand provide mechanisms and techniques that provide an external metric asthe primary tie-breaker in ISIS route selections. The presentlydescribed invention uses ISIS Type Length Variables (TLVs) and sub-TLVsthat are already defined by the standard to make route selectiondecisions based on external cost.

In a first particular embodiment of a method for providing an externalmetric as a tie-breaker for ISIS route selection, the method begins withidentifying a set of routes that are to be advertised by a router asexternal routes within a network. The method further includesadvertising the routes by the router using a Type Length Variable (TLV),wherein the TLV contains metric information to be used as a firsttiebreaker when selecting routes.

In a second particular embodiment of a method for using an externalmetric as a tie-breaker for ISIS route selection, the method includesreceiving, at the router, route advertisements within a network. Themethod also includes determining for a route advertisement if aparticular administrative sub-TLV is present in the route advertisement.When the particular administrative sub-TLV is present in the routeadvertisement then method includes using metric information in the TLVfor the route as a first tie-breaker when selecting between routes. Whenthe particular administrative sub-TLV is not present in the routeadvertisement then the method includes using internal ISIS Layer 1 (L1)cost as the first tie-breaker when making a route selection.

Other embodiments include a computer readable medium having computerreadable code thereon for providing an external metric as a tie-breakerfor ISIS route selection. The computer readable medium includesinstructions for identifying a set of routes that are to be advertisedby a router as external routes within a network. The computer readablemedium further includes instructions for advertising the routes by therouter using a TLV, wherein the TLV contains metric information to beused as a first tiebreaker when selecting routes.

In another particular embodiment the computer readable medium for usingan external metric as a tie-breaker for ISIS route selection, includesinstructions for receiving, at the router, route advertisements within anetwork. The computer readable medium also includes instructions fordetermining for a route advertisement if a particular administrativesub-TLV is present in the route advertisement. When the particularadministrative sub-TLV is present in the route advertisement then thecomputer readable medium includes instructions for using metricinformation in the TLV for the route as a first tie-breaker whenselecting between routes. When the particular administrative sub-TLV isnot present in the route advertisement then the computer readable mediumincludes instructions for using internal ISIS Layer 1 (L1) cost as thefirst tie-breaker when making a route selection.

Still other embodiments include a computerized device, configured toprocess all the method operations disclosed herein as embodiments of theinvention. In such embodiments, the computerized device includes amemory system, a processor, communications interface in aninterconnection mechanism connecting these components. The memory systemis encoded with a process that provides an external metric as theprimary tie-breaker in ISIS route selections as explained herein thatwhen performed (e.g. when executing) on the processor, operates asexplained herein within the computerized device to perform all of themethod embodiments and operations explained herein as embodiments of theinvention. Thus any computerized device that performs or is programmedto perform up processing explained herein is an embodiment of theinvention.

Other arrangements of embodiments of the invention that are disclosedherein include software programs to perform the method embodiment stepsand operations summarized above and disclosed in detail below. Moreparticularly, a computer program product is one embodiment that has acomputer-readable medium including computer program logic encodedthereon that when performed in a computerized device provides associatedoperations providing provide an external metric as the primarytie-breaker in ISIS route selections as explained herein. The computerprogram logic, when executed on at least one processor with a computingsystem, causes the processor to perform the operations (e.g., themethods) indicated herein as embodiments of the invention. Sucharrangements of the invention are typically provided as software, codeand/or other data structures arranged or encoded on a computer readablemedium such as an optical medium (e.g., CD-ROM), floppy or hard disk orother a medium such as firmware or microcode in one or more ROM or RAMor PROM chips or as an Application Specific Integrated Circuit (ASIC) oras downloadable software images in one or more modules, sharedlibraries, etc. The software or firmware or other such configurationscan be installed onto a computerized device to cause one or moreprocessors in the computerized device to perform the techniquesexplained herein as embodiments of the invention. Software processesthat operate in a collection of computerized devices, such as in a groupof data communications devices or other entities can also provide thesystem of the invention. The system of the invention can be distributedbetween many software processes on several data communications devices,or all processes could run on a small set of dedicated computers, or onone computer alone.

It is to be understood that the embodiments of the invention can beembodied strictly as a software program, as software and hardware, or ashardware and/or circuitry alone, such as within a data communicationsdevice. The features of the invention, as explained herein, may beemployed in data communications devices and/or software systems for suchdevices such as those manufactured by Avaya, Inc. of Basking Ridge, N.J.

Note that each of the different features, techniques, configurations,etc. discussed in this disclosure can be executed independently or incombination. Accordingly, the present invention can be embodied andviewed in many different ways. Also, note that this summary sectionherein does not specify every embodiment and/or incrementally novelaspect of the present disclosure or claimed invention. Instead, thissummary only provides a preliminary discussion of different embodimentsand corresponding points of novelty over conventional techniques. Foradditional details, elements, and/or possible perspectives(permutations) of the invention, the reader is directed to the DetailedDescription section and corresponding figures of the present disclosureas further discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 comprises a block diagram of a network in accordance withembodiments of the invention;

FIG. 2 comprises a flow diagram of a first method for providing use ofan external metric as a primary tie-breaker in ISIS route selections inaccordance with embodiments of the invention;

FIG. 3 comprises a flow diagram of a second method for providing use ofan external metric as a primary tie-breaker in ISIS route selections inaccordance with embodiments of the invention; and

FIG. 4 illustrates an example computer system architecture for acomputer system that provides use of an external metric as a primarytie-breaker in ISIS route selections in accordance with embodiments ofthe invention.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing embodiments of the invention. Upon readingthe following description in light of the accompanying figures, thoseskilled in the art will understand the concepts of the invention andrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

A particular embodiment of the invention will now be described withreference to the accompanying drawings. The invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiment set forth herein; rather, this embodiment is providedso that this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Theterminology used in the detailed description of the particularembodiment illustrated in the accompanying drawings is not intended tobe limiting of the invention. In the drawings, like numbers refer tolike elements.

FIG. 1 illustrates an environment 10 wherein a first access network 14and a second access network 28 are interconnected by way of a transportnetwork 16. Transport network 16 in this example is a network that usesISIS as a protocol to exchange Layer-3 routes. The transport network 16includes a group of network devices, 18, 20, 22, 24, 30, 32, 34, 36 and38.

Network devices 18,20,22,24, 32 and 34 are devices capable of runningthe ISIS protocol and capable of generating and processing ISIS TLVsthat are used to advertize Layer-3 routes.

Transport network 16 in this example is running the ISIS protocol.Router 18 is an ISIS router. On router 18, a set of routes that are tobe advertised by the router using ISIS are identified as external routesusing either explicit and/or default configuration settings (exampleroute-policies and implicit defaults within such policies). In thisexample the ISIS implementation on the router uses TLV#135 along witheither the 32-bit or the 64-bit administrative tag sub-TLV to advertisethe routes. Another ISIS router (e.g. router 30) in the network 16receives the route advertisement. At router 30, if the specific32/64-bit administrative tag sub-TLV is not present in the routeadvertisement then the internal ISIS L1 cost is used as the firsttie-breaker when making a route selection. On the other hand, if thespecific 32/64-bit administrative tag sub-TLV is present in the routeadvertisement, then the metric information in the route TLV is used asthe first tie-breaker.

This allows a network operator to inject routes into ISIS with differentexternal metrics and use the external metric as the first tiebreakerwhen selecting routes. By controlling the value of the external metricthe operator can then achieve the desired route selection behaviors.

It should be noted that while the above description uses TLV#135, thesame applies to the use of the 32/64-bit administrative tag Sub-TLVswith TLV#135, TLV#235, TLV#236 or TLV#237.

By controlling the metric on the router advertising the routes, the needto configure route-policies on all the routers in the network iseliminated. Further, unlike the use of the ISIS link metric—this istotally independent of the internal topology of the network and offersmuch better granular control of the traffic types that are impacted.

Flow diagrams of the presently disclosed methods are depicted in FIGS. 2and 3. The rectangular elements are herein denoted “processing blocks”and represent computer software instructions or groups of instructions.Alternatively, the processing blocks represent steps performed byfunctionally equivalent circuits such as a digital signal processorcircuit or an application specific integrated circuit (ASIC). The flowdiagrams do not depict the syntax of any particular programminglanguage. Rather, the flow diagrams illustrate the functionalinformation one of ordinary skill in the art requires to fabricatecircuits or to generate computer software to perform the processingrequired in accordance with the present invention. It should be notedthat many routine program elements, such as initialization of loops andvariables and the use of temporary variables are not shown. It will beappreciated by those of ordinary skill in the art that unless otherwiseindicated herein, the particular sequence of steps described isillustrative only and can be varied without departing from the spirit ofthe invention. Thus, unless otherwise stated the steps described beloware unordered meaning that, when possible, the steps can be performed inany convenient or desirable order.

Referring now to FIG. 2, a first particular embodiment of a method 50for providing use of an external metric as the primary tie-breaker inISIS route selections is shown. Method 50 begins with processing block52 which discloses identifying a set of routes that are to be advertisedby the router as external routes within a network. As shown inprocessing block 54, the network is running an Intermediate System ToIntermediate System (ISIS) protocol.

Processing block 56 states advertising the routes by the router using aType Length Variable (TLV), wherein the TLV contains metric informationto be used as a first tiebreaker when selecting routes. As shown inprocessing block 58 the TLV includes a at least one of the groupcomprising a 32-bit administrative tag sub-TLV and a 64-bitadministrative tag sub-TLV. As further shown in processing block 60 theTLV is selected from the group comprising TLV#135, TLV#235, TLV#236, andTLV#237.

Referring now to FIG. 3 a second particular embodiment of a method 70for providing use of an external metric as the primary tie-breaker inISIS route selections is shown. Method 70 begins with processing block72 which discloses receiving, at the router, route advertisements withina network. As shown in processing block 74, the network is running anIntermediate System to Intermediate System (ISIS) protocol.

Processing block 76 discloses determining for a route advertisement if aparticular administrative sub-TLV is present in the route advertisement.Processing block 78 shows the TLV includes at least one of the groupcomprising a 32-bit administrative tag sub-TLV and a 64-bitadministrative tag sub-TLV. Processing block 80 shows wherein the TLV isselected from the group comprising TLV#135, TLV#235, TLV#236, andTLV#237. Processing block 82 states when the particular administrativesub-TLV is present in the route advertisement then using metricinformation in the TLV for the route as a first tie-breaker whenselecting between routes. Processing block 84 recites when theparticular administrative sub-TLV is not present in the routeadvertisement then using internal ISIS L1 cost as the first tie-breakerwhen making a route selection.

FIG. 4 is a block diagram illustrating example architecture of acomputer system 110 that executes, runs, interprets, operates orotherwise performs an external metric operating application 140-1 andexternal metric operating process 140-2 suitable for use in explainingexample configurations disclosed herein. The computer system 110 may beany type of computerized device such as a personal computer,workstation, portable computing device, console, laptop, networkterminal or the like. An input device 116 (e.g., one or morecustomer/developer controlled devices such as a keyboard, mouse, etc.)couples to processor 113 through I/O interface 114, and enables acustomer 108 to provide input commands, and generally control thegraphical customer interface 160 that the external metric operatingapplication 140-1 and process 140-2 provides on the display 130.Essentially, the graphical user interface 160 is where the customer108-1 performs their ‘online banking’, specifying which bills are to bepaid electronically, when those bills are to be paid, and the amount tobe paid. As shown in this example, the computer system 110 includes aninterconnection mechanism 111 such as a data bus or other circuitry thatcouples a memory system 112, a processor 113, an input/output interface114, and a communications interface 115. The communications interface115 enables the computer system 110 to communicate with other devices(i.e., other computers) on a network (not shown).

The memory system 112 is any type of computer readable medium, and inthis example, is encoded with an external metric operating application140-1 as explained herein. The external metric operating application140-1 may be embodied as software code such as data and/or logicinstructions (e.g., code stored in the memory or on another computerreadable medium such as a removable disk) that supports processingfunctionality according to different embodiments described herein.During operation of the computer system 110, the processor 113 accessesthe memory system 112 via the interconnect 111 in order to launch, run,execute, interpret or otherwise perform the logic instructions of anexternal metric operating application 140-1. Execution of a externalmetric operating application 140-1 in this manner produces processingfunctionality in the external metric operating process 140-2. In otherwords, the external metric operating process 140-2 represents one ormore portions or runtime instances of an external metric operatingapplication 140-1 (or the entire an external metric operatingapplication 140-1) performing or executing within or upon the processor113 in the computerized device 110 at runtime.

It is noted that example configurations disclosed herein include theexternal metric operating application 140-1 itself (i.e., in the form ofun-executed or non-performing logic instructions and/or data). Theexternal metric operating application 140-1 may be stored on a computerreadable medium (such as a floppy disk), hard disk, electronic,magnetic, optical, or other computer readable medium. A external metricoperating application 140-1 may also be stored in a memory system 112such as in firmware, read only memory (ROM), or, as in this example, asexecutable code in, for example, Random Access Memory (RAM). In additionto these embodiments, it should also be noted that other embodimentsherein include the execution of a external metric operating application140-1 in the processor 113 as the external metric operating process140-2. Those skilled in the art will understand that the computer system110 may include other processes and/or software and hardware components,such as an operating system not shown in this example.

A display 130 need not be coupled directly to computer system 110. Forexample, the external metric operating application 140-1 can be executedon a remotely accessible computerized device via the network interface115. In this instance, the graphical customer interface 160 may bedisplayed locally to a customer 108 of the remote computer, andexecution of the processing herein may be client-server based.

During operation, processor 113 of computer system 100 accesses memorysystem 112 via the interconnect 111 in order to launch, run, execute,interpret or otherwise perform the logic instructions of the externalmetric application 140-1. Execution of external metric application 140-1produces processing functionality in external metric process 140-2. Inother words, the external metric process 140-2 represents one or moreportions of the external metric application 140-1 (or the entireapplication) performing within or upon the processor 113 in the computersystem 100.

It should be noted that, in addition to the external metric process140-2, embodiments herein include the external metric application 140-1itself (i.e., the un-executed or non-performing logic instructionsand/or data). The external metric application 140-1 can be stored on acomputer readable medium such as a floppy disk, hard disk, or opticalmedium. The external metric application 140-1 can also be stored in amemory type system such as in firmware, read only memory (ROM), or, asin this example, as executable code within the memory system 112 (e.g.,within Random Access Memory or RAM).

In addition to these embodiments, it should also be noted that otherembodiments herein include the execution of external metric application140-1 in processor 113 as the external metric process 140-2. Thoseskilled in the art will understand that the computer system 100 caninclude other processes and/or software and hardware components, such asan operating system that controls allocation and use of hardwareresources associated with the computer system 100.

The device(s) or computer systems that integrate with the processor(s)may include, for example, a personal computer(s), workstation(s) (e.g.,Sun, HP), personal digital assistant(s) (PDA(s)), handheld device(s)such as cellular telephone(s), laptop(s), handheld computer(s), oranother device(s) capable of being integrated with a processor(s) thatmay operate as provided herein. Accordingly, the devices provided hereinare not exhaustive and are provided for illustration and not limitation.

References to “a microprocessor” and “a processor”, or “themicroprocessor” and “the processor,” may be understood to include one ormore microprocessors that may communicate in a stand-alone and/or adistributed environment(s), and may thus be configured to communicatevia wired or wireless communications with other processors, where suchone or more processor may be configured to operate on one or moreprocessor-controlled devices that may be similar or different devices.Use of such “microprocessor” or “processor” terminology may thus also beunderstood to include a central processing unit, an arithmetic logicunit, an application-specific integrated circuit (IC), and/or a taskengine, with such examples provided for illustration and not limitation.

Furthermore, references to memory, unless otherwise specified, mayinclude one or more processor-readable and accessible memory elementsand/or components that may be internal to the processor-controlleddevice, external to the processor-controlled device, and/or may beaccessed via a wired or wireless network using a variety ofcommunications protocols, and unless otherwise specified, may bearranged to include a combination of external and internal memorydevices, where such memory may be contiguous and/or partitioned based onthe application. Accordingly, references to a database may be understoodto include one or more memory associations, where such references mayinclude commercially available database products (e.g., SQL, Informix,Oracle) and also proprietary databases, and may also include otherstructures for associating memory such as links, queues, graphs, trees,with such structures provided for illustration and not limitation.

References to a network, unless provided otherwise, may include one ormore intranets and/or the internet, as well as a virtual network.References herein to microprocessor instructions ormicroprocessor-executable instructions, in accordance with the above,may be understood to include programmable hardware.

Unless otherwise stated, use of the word “substantially” may beconstrued to include a precise relationship, condition, arrangement,orientation, and/or other characteristic, and deviations thereof asunderstood by one of ordinary skill in the art, to the extent that suchdeviations do not materially affect the disclosed methods and systems.

Throughout the entirety of the present disclosure, use of the articles“a” or “an” to modify a noun may be understood to be used forconvenience and to include one, or more than one of the modified noun,unless otherwise specifically stated.

Elements, components, modules, and/or parts thereof that are describedand/or otherwise portrayed through the figures to communicate with, beassociated with, and/or be based on, something else, may be understoodto so communicate, be associated with, and or be based on in a directand/or indirect manner, unless otherwise stipulated herein.

Although the methods and systems have been described relative to aspecific embodiment thereof, they are not so limited. Obviously manymodifications and variations may become apparent in light of the aboveteachings. Many additional changes in the details, materials, andarrangement of parts, herein described and illustrated, may be made bythose skilled in the art.

Having described preferred embodiments of the invention it will nowbecome apparent to those of ordinary skill in the art that otherembodiments incorporating these concepts may be used. Additionally, thesoftware included as part of the invention may be embodied in a computerprogram product that includes a computer useable medium. For example,such a computer usable medium can include a readable memory device, suchas a hard drive device, a CD-ROM, a DVD-ROM, or a computer diskette,having computer readable program code segments stored thereon. Thecomputer readable medium can also include a communications link, eitheroptical, wired, or wireless, having program code segments carriedthereon as digital or analog signals. Accordingly, it is submitted thatthat the invention should not be limited to the described embodimentsbut rather should be limited only by the spirit and scope of theappended claims.

What is claimed is:
 1. A computer-implemented method in which a routerperforms operations comprising: identifying a set of routes that are tobe advertised by said router as external routes within a network; andadvertising said routes by said router using a Type Length Variable(TLV), wherein said TLV contains metric information to be used as afirst tiebreaker when selecting routes.
 2. The method of claim 1 whereinsaid network is running an Intermediate System To Intermediate System(ISIS) protocol.
 3. The method of claim 1 wherein said TLV includes atleast one of the group comprising a 32-bit administrative tag sub-TLVand a 64-bit administrative tag sub-TLV.
 4. The method of claim 1wherein said TLV is selected from the group comprising TLV#135, TLV#235,TLV#236, and TLV#237.
 5. A computer-implemented method in which a routerperforms operations comprising: receiving, at said router, routeadvertisements within a network; determining for a route advertisementif a particular administrative sub-TLV is present in said routeadvertisement; when said particular administrative sub-TLV is present insaid route advertisement then using metric information in said TLV forsaid route as a first tie-breaker when selecting between routes; andwhen said particular administrative sub-TLV is not present in said routeadvertisement then using internal ISIS Layer 1 (L1) cost as the firsttie-breaker when making a route selection.
 6. The method of claim 5wherein said network is running an Intermediate System To IntermediateSystem (ISIS) protocol.
 7. The method of claim 5 wherein said TLV isselected from the group comprising TLV#135, TLV#235, TLV#236, andTLV#237.
 8. The method of claim 5 wherein said TLV includes at least oneof the group comprising a 32-bit administrative tag sub-TLV and a 64-bitadministrative tag sub-TLV.
 9. A non-transitory computer readablestorage medium having computer readable code thereon for providing useof an external metric as a primary tie-breaker in route selections, themedium including instructions in which a router performs operationscomprising: identifying a set of routes that are to be advertised bysaid router as external routes within a network; and advertising saidroutes by said router using a Type Length Variable (TLV), wherein saidTLV contains metric information to be used as a first tiebreaker whenselecting routes.
 10. The computer readable storage medium of claim 9further comprising instructions wherein said network is running anIntermediate System To Intermediate System (ISIS) protocol.
 11. Thecomputer readable storage medium of claim 9 further comprisinginstructions wherein said TLV is selected from the group comprisingTLV#135, TLV#235, TLV#236, and TLV#237.
 12. The computer readablestorage medium of claim 9 further comprising instructions wherein saidTLV includes at least one of the group comprising a 32-bitadministrative tag sub-TLV and a 64-bit administrative tag sub-TLV. 13.A non-transitory computer readable storage medium having computerreadable code thereon for providing use of an external metric as aprimary tie-breaker in route selections, the medium includinginstructions in which a router performs operations comprising:receiving, at said router, route advertisements within a network;determining for a route advertisement if a particular administrativesub-TLV is present in said route advertisement; when said particularadministrative sub-TLV is present in said route advertisement then usingmetric information in said TLV for said route as a first tie-breakerwhen selecting between routes; and when said particular administrativesub-TLV is not present in said route advertisement then using internalISIS Layer 1 (L1) cost as the first tie-breaker when making a routeselection.
 14. The computer readable storage medium of claim 13 whereinsaid network is running an Intermediate System To Intermediate System(ISIS) protocol.
 15. The computer readable storage medium of claim 13wherein said TLV is selected from the group comprising TLV#135, TLV#235,TLV#236, and TLV#237.
 16. The computer readable storage medium of claim13 wherein said TLV includes at least one of the group comprising a32-bit administrative tag sub-TLV and a 64-bit administrative tagsub-TLV.
 17. A router comprising: a memory; a processor; acommunications interface; an interconnection mechanism coupling thememory, the processor and the communications interface; and wherein thememory is encoded with an application providing use of an externalmetric as a primary tie-breaker in route selections, that when performedon the processor, provides a process for processing information, theprocess causing the computer system to perform the operations of:identifying a set of routes that are to be advertised by said router asexternal routes within a network; and advertising said routes by saidrouter using a Type Length Variable (TLV), wherein said TLV containsmetric information to be used as a first tiebreaker when selectingroutes.
 18. The router of claim 17 wherein said network is running anIntermediate System To Intermediate System (ISIS) protocol.
 19. Therouter of claim 17 wherein said TLV includes at least one of the groupcomprising a 32-bit administrative tag sub-TLV and a 64-bitadministrative tag sub-TLV, and wherein said TLV is selected from thegroup comprising TLV#135, TLV#235, TLV#236, and TLV#237.
 20. A routercomprising: a memory; a processor; a communications interface; aninterconnection mechanism coupling the memory, the processor and thecommunications interface; and wherein the memory is encoded with anapplication providing use of an external metric as a primary tie-breakerin route selections, that when performed on the processor, provides aprocess for processing information, the process causing the computersystem to perform the operations of: receiving, at said router, routeadvertisements within a network; determining for a route advertisementif a particular administrative sub-TLV is present in said routeadvertisement; when said particular administrative sub-TLV is present insaid route advertisement then using metric information in said TLV forsaid route as a first tie-breaker when selecting between routes; andwhen said particular administrative sub-TLV is not present in said routeadvertisement then using internal ISIS Layer 1 (L1) cost as the firsttie-breaker when making a route selection.
 21. The router of claim 20wherein said network is running an Intermediate System To IntermediateSystem (ISIS) protocol.
 22. The router of claim 20 wherein said TLV isselected from the group comprising TLV#135, TLV#235, TLV#236, andTLV#237, and wherein said TLV includes at least one of the groupcomprising a 32-bit administrative tag sub-TLV and a 64-bitadministrative tag sub-TLV.